1. Field of The Invention
The present invention relates to a control apparatus and method for automatically controlling a hydraulic system used on heavy construction equipment, such as on an excavator and the like, and more particularly to a control apparatus in which a driving engine of the hydraulic system is always optimally started, and the temperature of the hydraulic fluid for actuators in the hydraulic system is automatically controlled and also is preheated in order to reach to a predetermined temperature, thereby improving the operational effect of the hydraulic system and the construction equipment.
2. Description of The Prior Art
Conventionally, known hydraulic systems for heavy construction equipment such as an excavator or a hydraulic shovel drive system are provided with a plurality of hydraulic pumps which are driven by a diesel engine, the output hydraulic fluid being communicated to a plurality of actuators operably connected to buckets adapted to do work. Thus, a desired operation can be efficiently preformed by the heavy construction equipment.
However, the known hydraulic system for heavy construction equipment has the following disadvantages. When operated with the hydraulic fluid in either a cold or overheated condition, the hydraulic system operates roughly and in a manner not typical of the normal operating characteristics of the system. This results in fatigue to the equipment operator, the fatigue causing the operator and the equipment to provide a lower quality job than the heavy construction equipment is capable of. This also causes the driving power of the engine to be wasted by inefficiently moving overheated or underheated hydraulic fluid. Still further, the overheated or underheated hydraulic fluid results in rough movement of the actuators, causing the actuators to be broken and/or causing safety accidents to occur during use of the equipment.
The driving engines of the known hydraulic system for heavy construction equipment have to be preheated before starting normal operation. This is typical of many types of equipment and vehicles which have to be preheated in order to reach a desired operating temperature. However, it is especially true of the heavy construction equipment, since the hydraulic fluid has to be preheated before starting normal machine operation in order to allow the hydraulic fluid to achieve a desired temperature and operating viscosity.
However, the known hydraulic system for heavy construction equipment has no apparatus for sensing the temperature of the hydraulic fluid and no apparatus for controllably heating the hydraulic fluid to the desired temperature. As a result, the operator must use his experience to estimate or guess at the temperature of the hydraulic fluid after considering the ambient temperature and peripheral temperature around the heavy construction equipment. The operator must then preheat the hydraulic fluid of the heavy construction equipment for a time in order to raise the temperature of the hydraulic fluid to the desired temperature. Thus, the known hydraulic system for heavy construction equipment has a disadvantage in that the preheating operation for the hydraulic fluid is not optimally and accurately performed. For example, if the preheating operation is carried out for too long of a time period, the hydraulic fluid becomes overheated resulting in driving power loss and system inefficiencies. On the other hand, if the preheating operation is not carried out for a long enough time period, the temperature of the hydraulic fluid does not reach the desired temperature, resulting in the engine of the hydraulic system being overloaded due to the cold temperature of the hydraulic fluid.
Second, the known hydraulic system for heavy construction equipment is conventionally provided with a plurality of hydraulic pumps which are each connected to a drive shaft of the engine, and is also provided with a plurality of actuators which are driven by the hydraulic fluid outputted from the hydraulic pumps. In addition, the known heavy construction equipment is provided with several operational modes, each previously programmed in a control circuit. The control circuit allows the operator to select one of the programmed operational modes depending upon a given operational condition, the operational condition being a function of ambient temperature, the machine temperature, the prospective machine speed and work to be done, and the like. The operational speed of the hydraulic system of the heavy construction is varied depending on the selected mode and operational condition. However, if an improper mode is selected, the machine will operate at a less than optimal operational speed.
For example, a known hydraulic system for heavy construction equipment is disclosed in Korean Patent Application No. 90-15862, which application was applied for by the applicant of this invention. The hydraulic system is provided with three operational modes each previously programmed in the control circuit thereof. In a first mode, an "H operational" mode, a maximum quantity of fuel is supplied to the engine in order to drive the engine at a maximum rotative speed so that the operational speed of the heavy construction equipment reaches to a maximum operational speed. In a second mode, an "S operational" mode, the engine is driven at a normal rotative speed (which is about 10-20% below the maximum rotative speed) in order to accomplish a normal speed of operation. In a third mode, an "L operational" mode, the engine is driven at a still lower rotative speed (which is about 10-20% below the above-noted normal speed) in order to accomplish a quieter operation. During operation of the above known construction equipment, the operator selects one of the programmed operational modes, i.e. one of the H, S and L operational modes, by means of an operational mode select switch provided in the control cab. The operator preferably makes his selection depending on the operational condition expected.
However, if the heavy construction equipment is operated for a long time on the H operational mode, the respective temperature of the engine coolant and the hydraulic fluid is likely to exceed the predetermined maximum allowable overheat temperature. Hence, where the equipment is operated a long time under the H operational mode, the operator has to repeatedly and frequently check the respective temperature of the engine coolant and the hydraulic fluid and manually reduce the engine speed in order to prevent overheating. Furthermore, the operator may need to temporarily stop the operation of the heavy construction in order to cool or replace the overheated engine coolant with new coolant and in order to cool or replace the hydraulic fluid with new hydraulic fluid. Therefore, the known heavy construction equipment has a disadvantage in that a continuous operation may lead to an overheat condition which would undesirably affect the operation and efficiency of the equipment and potentially also undesirably burden the operator with changing the engine coolant and the hydraulic fluid.
Third, the hydraulic system in the known heavy construction equipment conventionally adopts a starting manner for the diesel engine in which a fuel supply control valve (a throttle valve) is first positioned at the starting position, and an engine starting switch (mateably engaged with an engine starting key) is then shifted from stop position to starting position in order to start the engine. After starting the engine, and the engine starting switch automatically returns to the stop position. However, the diesel engine has a disadvantage in that cold starting the engine is difficult, thereby resulting in multiple restart attempts. These multiple and extended restart attempts frequently lead to starter motor breakdown and dead batteries. In addition, the diesel engine requires a special "cold start" in case of starting under a cold temperature. In the cold start, the engine is either preheated for a time before the normal starting sequence in order to raise the temperature of the engine to a desired temperature, or an additive such as an ether is supplied to the engine before beginning the starting sequence. Thus, the known hydraulic system for heavy construction equipment utilizing a standard diesel engine arrangement has a disadvantage in that it can not provide reliability and quick start of the engine.